1. Field of the Invention
This invention relates to a process for the recovery of the gold, silver and selenium content of copper refinery slimes.
2. Prior Art
Copper refinery slimes are the insoluble residues from the anodic dissolution of anode copper that settle and accumulate as "anode mud" at the bottom of electrolytic copper refining cells. These insoluble metals and compounds comprise varying amounts of copper, silver, gold and selenium together with lead, tellurium, traces of platinum group metals, sulfur and other elements, depending on the initial composition of the copper ore and its subsequent treatment, and are a valuable byproduct of the electrolytic refining of copper.
The slimes are treated by various processes to recover the precious metals and other valuable constituents. As the composition of the slimes produced at various refineries varies considerably there is usually a considerable difference in the slime treatment flow sheet employed by each refinery. However, in almost all of the slime treatment processes heretofore employed the slimes are subjected to various pyrometallurgical refining steps to remove most of the non-precious metal constituents of the slimes and to obtain an impure gold-silver alloy known as Dore metal. The Dore metal is then subjected to an electrolytic refining operation to recover a relatively pure silver deposit at the cathode and a gold-rich anode mud that is further refined to obtain a pure gold product. In all of these prior art processes involving multiple pyrometallurgical refining steps there is significant recycling of metal-rich slags, and the the relatively large amount of material being processed and recycled represents a high inventory cost of precious metals tied up in the process.
After an intensive investigation into the problems and limitations of conventional processes for the treatment of copper refinery slimes, and in particular slimes of relatively high selenium content, we have now devised a new process for the treatment of these slimes that provides a clean separation of the valuable constituents of the slimes without tying up large amounts of these valuable constituents in metal-rich slags that must be recycled through the process. Our new process involves the removal of copper from the raw slimes by acid leaching under oxygen pressure, the removal and recovery of selenium by oxidation and volatilization, and the parting and refining of the silver and gold content of the decopperized and deselenized slime residue by hydrometallurgical procedures. Moreover, the process results in high recoveries of the selenium, silver and gold content of the slimes in pure form without significant recycling of or multiple purifying steps for the selenium and the precious metals.